1. Field of the Invention
The present invention relates to a method for manufacturing hydrochlorofluoroolefins. More particularly, this invention relates to synthesis of 2-chloro-3,3,3,-trifluoropropene (HCFC-1233xf).
2. Description of Related Art
Fluorocarbon based fluids have found widespread use in industry in a number of applications, including as refrigerants, aerosol propellants, blowing agents, heat transfer media, and gaseous dielectrics. Because of the suspected environmental problems associated with the use of some of these fluids, including the relatively high global warming potentials associated therewith, it is desirable to use fluids having the lowest possible greenhouse warming potential in addition to zero ozone depletion potential. Thus there is considerable interest in developing environmentally friendlier materials for the applications mentioned above.
Tetrafluoropropenes, having essentially zero ozone depletion and low global warming potential, have been identified as potentially filling this need. However, the toxicity, boiling point, and other physical properties in this class of chemicals vary greatly, even between different isomers of a compound. One tetrafluoropropene having valuable properties is 2,3,3,3-tetrafluoropropene (HFO-1234yf). HFO-1234yf has been found to be an effective refrigerant, heat transfer medium, propellant, foaming agent, blowing agent, gaseous dielectric, sterilant carrier, polymerization medium, particulate removal fluid, carrier fluid, buffing abrasive agent, displacement drying agent and power cycle working fluid. Thus, there is a need for new manufacturing processes for the production of tetrafluoropropenes and in particular 2,3,3,3-tetrafluoropropene.
One process for producing tetrafluoropropenes involves the use of tetrachloropropenes as a reactant (U.S. 2007-0197842 A1). Additionally, several other methods of preparing hydrofluoroalkenes are known. For example, U.S. Pat. No. 4,900,874 (Ihara et al) describes a method of making fluorine containing olefins by contacting hydrogen gas with fluorinated alcohols. U.S. Pat. No. 2,931,840 (Marquis) describes a method of making fluorine containing olefins by pyrolysis of methyl chloride and tetrafluoroethylene or chlorodifluoromethane. The preparation of HFO-1234yf from trifluoroacetylacetone and sulfur tetrafluoride has been described. See Banks, et al., Journal of Fluorine Chemistry, Vol. 82, Iss. 2, p. 171-174 (1997). Also, U.S. Pat. No. 5,162,594 (Krespan) discloses a process wherein tetrafluoroethylene is reacted with another fluorinated ethylene in the liquid phase to produce a polyfluoroolefin product.
Notwithstanding prior teachings, applicants have come to appreciate a continuing need for methods of efficiently preparing intermediates of certain hydrohalocarbons, particularly compounds which are in part useful as intermediates in the preparation of tetrafluoropropenes, such as 2,3,3,3-tetrafluoropropene (HFO-1234yf).
The prior art discloses various processes for the preparation of polyhaloolefin products that involve separate steps as well as disparate reaction conditions, reagents, and catalysts. The efficiency of such multi-step processes is thus limited by the efficiency of each individual step. As such, one inefficient step may make the entire process more resource intensive, less effective at converting intermediates to the desired fluorocarbon products and less productive, suffering yield losses due to increased impurity formation.
The present invention offers a less resource-intensive process that produces increased conversion of intermediates to the end product polyhaloolefin over a longer period due to substantially increased catalyst life. This is achieved by Applicants' discovery of subjecting a tetrachloropropene to fluorination with a fluorinating agent and a catalyst in the presence of a stabilizer.